Forum » General Tuning Discussion » Advice on tuning a Botched Job

Advice on tuning a Botched Job

General Tuning Discussion

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads

Page 1

Hi All,

After a couple of months with successful tuning and basic street builds, I have run into a situation where I have made a mistake on my own vehicle during the build process.

On an elite 2500 on an EJ257. The issue being the compression ratio is totally not what was desired. Typical street build except the head gaskets were too thick and brought it into the 7.8-7.9:1 range. Before the build it was an 8.2:1 ish after the skim job and ran ethanol and made such easy power on a 3576R. 26psi was putting down slightly over 500whp with conservative timing.

Fast Forward to after the refresh and the same map only put out 450ish on the same dyno and same boost and ambient conditions.

With a Lower CR, is it typical to need more timing and than usual to combat the high EGTS and stabilize the boost control setup? Would this setup make more sense and power on a lower octane fuel(volatility) ex. 91oct or 93oct? Or do just assume that i just need to keep upping the boost ignition to maintain the same Cyl pressures as the original build on e85? i totally fudged myself.

50hp sounds like a huge loss for a relatively small loss in compression. Have you verified things like can timing and ignition timing after the motor was assembled and installed?

Does it still drive alright? Does it really feel like it's down on power? Does it feel lazy everywhere or only in the top end ?

I have not gotten completely done with the cam timing. However while on the Dyno, i left the same main ignition map the same while redoing the boost control and then i could not for the life of me get it to stabilize at all until ramped the timing up ALOT to bring the climbing EGTS down.

I did everything in the usual order of the 10 step process and ran out of dyno time at 140ish KPA due to diagnosing the crazy egts. But now that you mention cam timing, i wonder if it changed as much as the main ignition did due to lower cylinder pressures with the change in static CR.

It drives alright off boost still. it definitely feels down on power. everywhere from spool to peak torque to top end is down. I also have some spark break up or blowout on the top end past 6500rpm. Previously it revved to 7500rpm. nothing different here just literally too thick of a head gasket on an ej257. went from a cometic .039 "to an Athena cut ring .051" with the inox steel rings.

I'm not familiar with the 10 step process. Have you verified ignition timing with a timing light?

I do very little with Subaru stuff but it sounds like one of your cams might be a tooth out (easy to do on a Subaru) potentially meaning your triggering and therefore ignition timing will be out substantially also.

Timing on the Crank and all cam gears line up with the marks and also matches the standalone. there is very little filtering applied and i get little to no trigger errors in daily usage. im pretty sure everything is in order minus the cam timing possibly.

There will be a very small decrease in net dynamic compression, so might benefit from a tiny bit more advance - but I fail to see how that can cause such a power loss.

I'm also not familiar with the Sub' engines, but as has been said, if you've checked everything else, it could be a cam' out a tooth. If that' s a apin to check, I'd go back over everything I did, from filter (if used, to the head, and from the head to the tailpipe, and I' d also double check the actual and programmed TDC match up.

In the meantime, that electrical problem needs to be addressed ASAP, as it is not only costing you torque/power, but it's going to be messing up your lambda and apparent AFR numbers. That is to say, a misfire will result in the lambda reading un-used oxygen in the exhaust gases, which it reads as a lean mixture, and you, or the ECU, may be adding fuel to try and correct it, causing an excessively rich mixture.

A high EGT, if the mixture is correct, is normally caused by retarded ignition resulting in the combustion process continuing into the exhaust opening point and, contributing towards it, less cooling of the charge from the expansion in the power stroke from the piston moving down the bore. Another reason to double check the ECU and actual TDCs actually line up.

If you have access to an IR camera, or even use the old school water spray bottle, check to see if one bank has a higher/lower exhaust manifold temperature - that may indicate one camshaft is incorrectly times.

After pulling the front cover and putting a timing light to it with the laptop nearby. Everything seems to be mechanically in order. Ran a boost leak test and the pressure drops at a slow rate of .5 psi/sec. The marks all still line up. Im wondering if the dwell times in the ignition table are wrong but it would be unlikely as they are just basic 3.5ms subaru grey coil packs.

As far as the egts go, they are now under control with the additional timing. As a result, the boost is now stable and PID controls are reacting predictably. Have tuned out to 24.5psi but it seems down on power still and still having issues with break up past 6500 rpm. I will be adding a few more chassis grounds to the block and main ecu ground to suppliment existing. My though is that with the lower dynamic compression ratio on pump e85 the flame front is traveling slower coupled with the slower piston speed causing a torque reduction. From 4500-6500 it seems to be happier.